1. Field of the Invention
The present invention relates to a method of calibrating and a calibration apparatus for a moisture concentration measurement apparatus that measures the moisture concentration in a gas using a light source.
2. Description of the Related Art
Conventionally, the combustion exhaust gas discharged from a boiler that burns coal, heavy oil, and the like contains components such as NOx, SOx, CO2, and CO. Furthermore, gas analysis apparatuses have been developed that analyze the content of these components in a gas. An example of such a gas analysis apparatus that has been developed is one that employs a probe. In a probe type gas analysis apparatus, a measuring beam emitted from a light source is caused to be reflected by a reflector, which is disposed in a tip part of the probe, and the concentration of a prescribed component in the sample gas is analyzed based on information from the measuring beam reflected by the reflector.
In addition, an example of a known probe type gas analysis apparatus is one that comprises a calibration function in addition to a component concentration analysis function.
However, the calibration of a gas analysis apparatus is problematic when measuring the concentration of moisture at 0 degree in Celsius saturation or greater, such as, for example, moisture in an exhaust gas after a combustion process and an exclusion treatment process that uses an aqueous solution. In particular, if calibration is performed using moisture of a high concentration, such as when the dew point is room temperature or greater, then all pipings wherein the gas flows and that include the measurement area must be maintained at the temperature of the dew point or greater. It is difficult to install such calibration equipment in an actual equipment environment, even if it is possible to prepare an environment like that of a laboratory.
To solve such problems, a calibration apparatus for a laser type gas analyzer that can measure moisture concentration has been proposed (refer to Japanese Unexamined Patent Application Publication No. 2010-96561). This apparatus comprises a light emitting unit 250 and a light receiving unit 260; furthermore, a signal processing circuit measures the concentration of a measurement target gas by detecting the second harmonic signal of a modulated signal of a light source unit 204 based on an output signal of a light receiving unit 207. Provided are a piping 301, which hermetically connects both units 250, 260 and maintains a prescribed optical path length of a laser light, a gas washing bottle 500, which supplies air of a prescribed moisture concentration into the piping 301, and an oxygen meter 400, which measures the oxygen concentration of moisture-containing air supplied into the piping 301. The apparatus converts the measured oxygen concentration to moisture concentration, and, using this moisture concentration and the optical path length, calibrates the moisture concentration measurement value produced by the gas analyzer.
In the moisture concentration calibration apparatus recited in Japanese Unexamined Patent Application Publication No. 2010-96561, oxygen concentration before and after bubbling is measured in order to compensate for the concentration of gas generated by the bubbling. However, in this case, the actual calibration procedure is problematic because the calibration apparatus must be transported to the site.